only one AddressGroup in the AddressBook possible ?

Hello,

in the past(other email-products) we are used to have different-
AddressGroups in the "global-email-addressbook". Some users are
stored even in different groups. Users do easily understand that
concept.

1.
As I understand within Zimbra there is only 1 AddressBook possible.
Is that the case?
2.
Are personal distribution lists Zimbra's approach to address that
requirement?
3.
How are personal distribution-list visualized? In the AddressBook or
only if a new mail is written?